INSPECTOR SYSTEMS makes nozzle maintenance in steam generators possible. Technical installations that are subject to special safety criteria must always be kept at the best possible level of safety. This applies particularly to nuclear power stations with their innumerable pipelines systems required for operation and safety.
Keeping the individual pipeline sections in perfect condition is a decisive prerequisite for the safety of the entire installation. They therefore have to undergo strict and regular tests of various types.
This ensures that any damage to the pipes as a result of wear, corrosion, erosion and cracking is detected at an early stage. If a possible damaged point is detected it must, if not accessible in any other way, be repaired from inside with suitable rehabilitation means.
This requires manipulators with special know-how that provide the highest level of reliability and precision. For this INSPECTOR SYSTEMS has developed three special grinding robots, which after a development period of four months and an almost six-month qualification period were used in the renovation of steam generator nozzles of a pressurised water reactor at the turn of the year. On behalf of AREVA AP three nozzles were renovated from inside during the routine overhaul.
In the area of steam generator nozzles two different materials come into contact. The nozzle material differs from the continuing pipe. An optimum connection between the two materials was implemented by welding in an additional gladding in the connection area during the construction of the nuclear power station.
On the basis of routine maintenance and modernisation measures the operators of the pressurised water reactor decided to renew the strongly stressed points in the area of the gladding and replace them with a welding material specially selected for this area of application.
In order to be able to do this the existing gladding on the complete inner circumference of the pipe had to be carefully removed.
For this filigree work INSPECTOR SYSTEMS developed three equivalent grinding robots under complex technical and spatial framework conditions. These made it possible to prepare the required groove measuring 85 mm in width and 4.5 to 6 mm in depth. The welding material was then applied into this groove. The robots can also produce local area with a depth of 16 mm point by point according to precisely defined geometries.
The particular difficulty in developing the grinding robots lay in the fact that the robots had to be pulled with the aid of an insertion device through the manhole of the steam generator with an inner diameter of approx. 350 mm. Only then was it possible to work on the nozzles with an inner diameter of approx. 800 mm.
The large difference in diameter between the two scenarios required a completely new type of grinding robot design with variable telescopic cylinders for positioning the grinding motor and the centring/clamping unit, and also a high degree of rigidity of the entire system due to the active forces of the long lever arm of the grinding motor unit.
Due to the outstanding success of the overall project the renovation of steam generator nozzles at similarly constructed nuclear power stations is to be carried out by INSPECTOR SYSTEMS know-how.